The present invention relates to a universally applicable electromagnetic relay.
A relay contact spring must generally accomplish two tasks. On the one hand it supports a switch contact, which is pressed against a fixed contact via the spring force of the contact spring, on the other hand it is via said contact spring that the current is conducted to the switch contact. Whereas in the first case mechanical loading ability is of significance, the second task requires high electrical conductivity. Materials which exhibit high flexural strength in order to resist high mechanical loading, however, exhibit low conductivity and vice versa. If the relay is to generate large currents, the forward resistance is generally too great due to the poor conductivity of the contact spring and an additional flex must be provided to conduct the current to the movable contact.
A simpler method to reduce forward resistance of a relay is either to design the spring as particularly wide or to use a material exhibiting good conductivity. The latter variation, however, requires the mechanical loading of the spring to be relatively minor. The spring can be arched to this effect in order to uniformly distribute the ensuing bending stress.
A relay comprising an arched leaf spring is already known from DE 36 40 737 C2. Said spring is fixed at one end to a magnet yoke and at the other end to a plane side of the armature. A projection of said leaf spring supports a switch contact. Mechanical loading of the spring material is significantly higher in the region close to the fastenings than it is in the middle of the spring. Consequently, an arched shape of this type is suitable only in as far as it enables, through low mechanical loading of the spring material, the use of a material with high electrical conductivity.
It is the aim of the present invention to provide an electromagnetic relay with a low forward resistance without the need for additional components or an increase in structure size.
According to the invention, this aim is realised by a relay featuring the following characteristics:
a base body,
a coil,
a core arrangement,
an armature, which at one armature end is pivotally arranged around an armature rotational axis to an end section of the core arrangement and the other end of which forms a free armature end,
at least one fixed contact,
a contact spring, which is attached at one fastening end to an immovable section of the relay, comprising a movable contact spring end, which is coupled to the free armature end, and comprising at least one switch contact, which cooperates with at least one of the fixed contacts, whereby the contact spring is generally overall arched and designed as a momentum spring and whereby the switch contact is arranged at a middle section of the contact spring.
The relay according to the invention is advantageous due to the mechanical loading of the contact spring being very low and uniform. This is achieved primarily through designing the contact spring as a momentum spring. A momentum spring can be defined in that both spring ends are attached to third parts in such a way that no rotation of the spring end takes place to each third part around the fastening point.
Due to the movement of the free armature end, a torque is applied to the contact spring. Both spring ends are fastened in a torque-resistant manner.
The contact spring has the characteristic feature that the deformation of the spring during movement occurs in such a way that bending modification is almost constant. On this basis, the bending loads of the contact spring are, to a large extent, constant along the spring. The mechanical loadings of the spring are also low due to the large length of the contact spring. This is the case when the free contact spring end is fastened to the free armature end.
The low loading in the region of the contact spring ends is ensured in an advantageous manner in that the fastening plane of the movable contact spring end lies tangential to the moving direction of the free armature end, since as a result the spring is merely incidentally bent at the fastening point. There is equally an advantage when the fastening plane of the fastening end is essentially perpendicular to a very short connecting line extending from a fastening edge, on which the movable part of the contact spring commences, to the armature rotational axis.
The forward resistance is furthermore reduced, if the switch contact is arranged in a middle region of the contact spring, since as a result the current path is shortened from a linking connector to the switch contact. This arrangement has the additional advantage that a path transformation occurs from the free armature end to the switch contact and the contact opening forces of the switch contact are increased in comparison to an arrangement close to or beyond the armature end. In combination with an armature comprising a particularly large opening angle and thus covering a large path when closing, a weaker design of the magnet system is possible, at the same supporting a compact structure. As a result, an even weaker material can in addition be used for the contact spring, since the required restoring force is lower.
A particularly advantageous embodiment describes the contact spring in the form of an elliptical section, as in this embodiment the loading is distributed particularly uniformly over the length of the contact spring.
A further advantage follows from the armature rotational axis being positioned in approximately the middle of the region described by the contact spring, since as a result the free armature end is guided on a circular path, which subjects the contact spring to a particularly gentle stress, as a homogenous loading distribution ensues for the contact spring. The following applies for a substantially arched spring: if the form of the spring approaches that of an arc, the arc""s central point would correspond to the rotational axis.
An additional advantage of the invention follows from the contact spring being simultaneously able to bias the armature into a resting position, thus dispensing with an armature restoring spring.
The production of a contact spring for a relay according to the invention is particularly straightforward if the contact spring exhibits a constant width over its entire length and if for instance boreholes can be allotted at particular points for alleviating the load of the contact spring.
The contact spring is preferably made out of a highly electrically conductive material, the mechanical characteristics of which are nevertheless sufficient on the basis of the uniformly low mechanical loadings.
Further details of the embodiments of the invention are described in the subclaims.